Flow control valves of many kinds have been known but as far as applicant is aware, all have been subject to one or more serious limitations. Some valves have exhibited poor accuracy. Some have exhibited acceptable accuracy over only a limited dynamic range. Some have failed to provide a positive definite neutral position at which there is truly zero flow for a zero input signal. Some valves have required one or even two pressure regulated power supplies. Some valves have required external feedback connections.
It is an object of the present invention to provide an improved flow control valve in which the rate of output fluid flow follows an input signal closely over a wide dynamic range.